Although a pet needs to go outside to exercise and enjoy a natural environment, it is considered inhumane to leave a pet outside during a storm and during cold weather conditions. However, pets do not always come to a call. Pets and especially cats are known to roam in a backyard and hide. It is therefore difficult for a pet owner to call a cat inside upon hearing a weather forecast. It is also difficult to predict the exact time that a pet will be at the door waiting to come in.
This problem has been addressed by a number of inventors in the past. For examples, several electrical door chimes have been designed for operation by a pet, either by pressing on paw lever or by rubbing its body against a plate-like actuator. The following documents described electrical door chimes for pets.    U.S. Pat. No. 4,400,696 issued to Robert R. Klingensmith on Aug. 23, 1983;    U.S. Pat. No. 4,686,504 issued to Richard W. German on Aug. 11, 1987;    U.S. Pat. No. 5,303,677 issued to George D. Jones on Apr. 19, 1994;    U.S. Pat. No. 5,604,478 issued to Tamara L. Grady et al., on Feb. 18, 1997.
Another pet annunciator has been found in the prior art. This device is described in the following document:    U.S. Pat. No. 5,038,703 issued to Roberta K. Frush on Aug. 13, 1991.
This publication described a strip of vinyl lacing, to which are attached several sleigh bells. The strip of vinyl lacing is attached to a door knob such that when a cat climbs on the strip of vinyl lacing, the sound of the bells alerts the pet owner of the presence of the pet outside the door.
In yet another pet annunciator, a ball is attached to a string and suspended to a door knob. As understood, the movement of the ball against the door, when a cat is playing with the ball, alerts the pet owner inside the house. This device is described in the following document: U.S. Pat. No. D672,514 issued to Miraculous Dyer et al., on Dec. 11, 2012.
Although the door chimes and pet annunciators found in the prior art deserve undeniable merits, it is believed that a cat is not always attracted to a ball. It is believed that some pets can never be trained to press a paw switch. Furthermore, it is believed that a cat has no desire to jump and climb on a vinyl lacing when it is cold and raining outside. When the outdoor conditions are unfavorable, a cat tends to bundle up on itself, to puff up its fur and to lay still to conserve energy.
Therefore, it is believed that there is a need in the field of pet door knockers for an efficient design that has appeal to cats and that is easily operable by most cats. It is believed that there is a need in the field of pet door knockers for a door knocker that does not require a cat to jump, to climb or otherwise spend a lot of energy.